a) Field of the Invention
The invention relates to a method for the measurement, orientation and fixation of at least one single crystal and an apparatus directed thereto.
b) Description of the Related Art
It is well known that single crystals must be severed along cutting planes having a given orientation to the coordinate axes of the crystal lattice for application in the semiconductor industry and optics industry.
It has already been recognized that the determination of crystal orientation required for this purpose, i.e., the relationship of the crystallographic axes to the geometric axes and the given positioning of the single crystals relative to the cutting plane of a cutting device, e.g., a wire saw, outside of this device affords considerable advantages.
It is known, for example, from EP 0 802 029 B1 to fixedly arrange a plurality of circular-cylindrical single crystals successively in alignment with one another on a cutting support outside of the cutting device by means of a rotationally and translationally adjustable receiving device in such a way that the single crystals can be cut simultaneously in defined directions relative to the crystal lattice by means of the cutting device.
However, when very hard single crystals, e.g., sapphire or silicon carbide, are to be prepared by the device for simultaneous cutting in a multiple wire saw, a device of this kind is poorly suited because faulty cutting can result when the cutting wires pass through the free spaces remaining between the single crystals that are fastened to the cutting support due to tensions occurring in individual cutting wires.
Further, it is disadvantageous that the suggested method and the device depend on the measured single crystals being in fact arranged on the cutting support with the required accuracy. At least subsequent checking is ruled out because, after they are fixed on the support, the single crystals lying on the inside are no longer accessible to the end face measurement provided for the single crystals.
Another problem consists in that the x-ray diffractometer, which is normally used to determine crystal orientation and by means of which, e.g., according to JP 09-033456 A, the orientation of two lattice planes is determined one after the other by a theta scan, cannot work with the accuracy required for certain applications. One reason for this is that the required absolute relationship between the two measurements cannot be produced with sufficient accuracy.
Some of the applications in which the required cutting accuracy is appreciably higher than that required in silicon chip fabrication, for example, are the manufacture of white light emitting diodes, which are already being used in headlights for motor vehicles and will someday also be able to replace incandescent and fluorescent lamps, and the manufacture of light emitting diodes for data storage which emit in the blue and ultraviolet spectra. When sapphire or silicon carbide are to be used as substrates for producing components in this way, an increased accuracy of the surface orientation is crucial for the growth quality of the functional layers, generally based on gallium nitride, due to the required heteroepitaxy.